Typescript : how to create a type from a javascript object

Question

I want to create a type or an interface with typescript from a javascript object that I don't know how it's created.

for example I want to create a type Request to use it in my function so I can make sure I pass the right parameter to the function :

let req = require("somewhere"); // my javascript object

function myfunction(request : Request) {
// some code
}

myfunction(req);// ok
myfunction(20);// Error

how can I create the Request type

Answer 1

You can use the typeof keyword.

function myfunction(request : typeof req) {
// some code
}

Though be careful, if req is any you won't receive the type checking you want.

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That said, if you want to access the request interface defined in express I believe you can access it as follows

import express = require('express')
function myfunction(request : express.Request) {
// some code
}